Insulating rim joist area with gap

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  #1  
Old 05-23-17, 01:16 PM
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Insulating rim joist area with gap

Hello everyone,

I'm working on a room on the ground level which is partially below grade. (Building is a side split - late 70s). I would like to insulate my rim joist pockets with 2" foam board sealed with expanding foam.

My dilemma: The wooden sill plate doesn't run from the top of the inside wall all the way to the back of the joist pocket - there is a 1.5" gap between the inside of the inside wall, and the inside of the exterior brick. So the joist pocket "floor" or sill plate, isn't continuous from front to back. Looking down, I can see the inside of the exterior brick wall down to the concrete foundation.

(See attached images)

My idea: I don't want to fill this gap, I just want to cover it - possibly with 6 mil poly to prevent any moisture from reaching the back of the joist pocket behind the foam board.

Can any one comment whether they've seen this before, and whether my solution is appropriate / needed?

Thank you.
 
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  #2  
Old 05-23-17, 02:03 PM
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Welcome to the forums! The sheetrock is glued directly to the concrete block?? Poor choice, but the cards are dealt. I would pick up some Roxul Safe n Sound rock wool insulation in batts and cut the batts to fit down into the opening, then finish out the top with your foam and foam against the band. I would also continue the Roxul from the foam out 3 1/2" as an added measure of insulation.
 
  #3  
Old 05-25-17, 06:40 AM
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Thank you, do I need to maintain an air gap for the exterior brick veneer. In the picture, the brick shown is the inside of the exterior brick wall.
 
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Old 05-25-17, 07:01 AM
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Not if you insulate with Roxul. It is waterproof, fireproof, vermin proof and mold proof, and needs no vapor barrier.
 
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Old 05-25-17, 07:12 AM
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Great, thank you for this - this helps!
 
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